Manufacture of ethylene glycol



April 17, 1956 J. M. BROOKE 2,742,505

MANUFACT-URE OF' ETHYLENE. GLYCOL Filed Nov. 9, 1951 ETHYLENE GLYCOL 4 TTORNEVS ffJe's'siMtlBrokeg'SWeenyTeLyassignor t 'Phillips Petrot leumompany, ascorporation `'of Delaware "'pplicaonjnoyexbejr 9,'.194s1.seriaiN. 255,678 'f .1 eurams. liteit-22604635) This invention-relatesjto ethylene-iglycolyand to its 4reproduction. -In aipa'rticular aspect Athe instant invention relatesto a"process"for-preparingethylene glycol/'by the toxidation- 'oft ethylene. v

The lmostcommon-method'l for vpreparingfethylene 1f'glycol'commerically is= :the: chlorohydrin processVv `wherein Flf'e'thylene is'reacted lwith chlorine to `form. ethylene chloro ilhylrin Theresulting-'ethylene 'ohlorohydrin' is then hy- "'drolyzedI tofgive ethyleney glycol. 'f''IThe'1 present-invention @i is` concernedr v -withT the direct" oxidation of, ethylene with Ioxygen to produce ethylene rox-ide and zto the vproduction of 'ethyle'nelglycol therefrom, p "'When `"ethylene" glycol is f prepared by-the direct oxida- Mltio'rro A:ethylene"v'v'itlrair-"offxygeny ethylene' oxide is ""forniedfwhichcan'behyd'rolyz'edto ethyle'neiglycol. l To t `v`-forrr`1"-'the ethylene =o r`ude",='ffethyleneandairor oxygen are 'reactedi at-lan-elevatedi-temperature a'ndxf'in' the presence *fof4 an-oxidation-promot-i'ngI ca'talyst. f 'Ordinarily ethylene is mixed withalarge excess of ain-enoughto maintain the concentrationL 1belovv'the explosive limits,VVV and the gas "-m'ixture istintr'oduoed into a catalytic converter inwhich E"thetemperature iSi-caiefuIlycontrolled atfthe optimum "ftemperature, f' While 'reactions within thel explosivelimits "fareoperablel to'carry/outf this invention;l and are'l de te. s'ribed in" the-'--sec'ondl"and thirdv paragraph -be1ow,v they arejnot preferred for com-mercial'oper'ations oflarge: scale 5'equipment?tbecause.1l offffthe *constant* precautions -then 'Jeneededto---assurethattheignition temperature off545 i Cf: is heverreached in-` any `p'rtion of- 'ther apparatus fcontaining-'theexplosivemixtureil: By/operating below the t ""ftion.

` The temperature employed in the prparation of ethyl- Wrene oxideis'4 iti-"fthe rrige'rom'f150"' C; to' '400 C. "i However-temperatures as 4flow' as'-'100-C.have been used. Although the'temperaturewillldependjupon'the activity of the'icatalystsjthe `ethylene and v oxygen concentration, 'i"and/the"space-"velocity, 'a'desirableftemperature `range is rii'ror'r'r"200 C.'A t6`l300 C. "The 'ratiof of Jair' toiethylene has af' very` pronounced reiectonrconversion*"In addition, a" 'high -air to fethylene Iratio isI most'favorabletorobtainingboth good yields vand "'convei'sions.' However 'as'the catalyst ages it becomesless .and lessi'ecient forftheproduction of ethylene oxide. On continued?usi'theitemperature'of operation'of the talyst"must"b'e"rised if :maximum 'efficiency for Ythe .'f production of'eth'ylene' 'oxide is to be'maintainedfj Thus "Ij'forlgood' yields alhigh air 'toi ethylene' ratio must be aiii't'ai'ed, ythe .yield risingrapidlyuntil-the 'volumeratio I` o'ffreactants' becomes`aboiit '7 :1' to'zl. Nofpim'provelutioni can-bel evaporated tov 90-percent`glycolconcentra- 2,742,505 #Patented Apr. 17, 195e mentfin yield isi-realized. atf--ratiosy above. :1. JIt is therefore desirable 1to1 operate at ratios above about 8:1. However, the-permissible-.y ethylene t concentration:..fo'r a Ynonexplosive'mixture is s'etbyf' the lower explosive ilirhit 5 iwhich is 3 .4 volume per cent. .f jTherefore volume -percents l fl'ofA air greater tthan '9 6.6% have been used in'- thefreacti'onl mixture-@to provide the -dilution necessary to keep =be1ow -fsaid explosive Vlimit Further dilution is electedmbygire:v

10;'eOn`centrationl-o ethylene. Buildup lof'vinert gases in he systemllmay 4becontrolled Yby bleeding apar-tionv vofi A"e fi recycle-gas. 3Further-controler' concentration fof ethyl-r f ene and -of -fthe amount lof# air employed can .be obtained by stagewise addition of ethylene to? the reactingfzgaa 'sp'artof; the=ethylene1being added with-theinitial air and further portions being-added after'conversioniof a 'portion' of '.the-eth-yle'nein thel reaction mixture. -Pressure f has little-feie'ctonthe process,`soatmospheric orslightly superatrnospherict pressures' are f employed.A f

The' optimum `space velocityy is a `rfunction Soi-.the -activity'ofVV the catalystandy the/.temperature.ofoperation.

i-ffFor' `a ldefinite air to ethylene ratioas 'the `cozntactftime becomes/shorter# the temperature .of operation ofthe f catalystmusttbe raised if maximum conversionsfarettolbe "'obtained. "Byway ofexfampleiwith acatalysthprepa'red h bycoatingY coruhdunrfavith silver oxide; andl @with ariifair f *Lto'ethyleneratioi'ofz'llO-to ll'if-the contacttimelis from 42731Jto 5.'10 seconds'rthe temperature for optimum-conn-versioi1-should be-frornlabout 250? C. to l'about-270? C. "Q If the contact time isfrom 1":'14 to 1.25 seconds thenrthe f v terr'1per'ature:for- Voptimum .conversion should be' front` say time inithefrange'f'of 0.5610 0.60 second the temperature Y ,rr-*porous reactor `withina cooling chamber containingfidilute 'Lftfsulfuricfacidas 'thecoola`r`1t, and passing*y the "ethylene -oxide tso-formed-throughf the sulfuric acid` coolant* to for'methyleneglycol.

` --In-oprder^ to provide a better understanding "ofwth'ef in- `vention-the*accompanying drawing is provided which shows' two yreactors of the type contemplated herein. 'Figures 1' andfZ-fillustrate they invention with 'two different' typesof catalytic xrea'ctors.

In Figure -lreactor 1-is inthe form of a porous vtube Vfwhichis 'withinvichamber 2 containing a dilutesulfuric 'v acid coolant. -'Theethylene-oxygen reactor is also shown incrosssection in; Figure 1. In the embodiment shown therein the' reactor is an ordinary porous reactionltube jlledpwith catalyst 3.' Another embodiment of theinvention is;y shown in Figurev 2. In Figure 2 `the 'reactor within chamberhla comprises an` outerporous tube 1a and an inner perforated tube 4 designedl vfor better gas distribution. The catalyst 3a 'inl-ligure 2 is placed betweenthe tubes 4'and 1a. 6'5 It is.,l ofl course', understood that one or rnorejethylene yoxygen'reactorscanbe Vdisposed within asingle cooling 1 chamben` lIn another embodimenty of the invention the "ethylene-oxygen reactor employed within ythe cooling l 4vchamber can be impregnated with the` silver.y o 'other catalyst; for example the ethylene-oxygen (or' airl)freactor can be made of porous alundum impregnated with y. silver. y On the other hand, only .theinnersurface of .the

' oxide are metallic oxidation promotors. be in a pure form or, more desirably, on a support.

' borundum, and fused alumina.

3 reactor can be silver impregnated, kand not the outer surface.

The catalysts employed in the manufacture of ethylene The metals may Examples of suitable supports are pumice, glass, car- Among the metals which have been tried are platinum, iridium, osrnium, tantalum, tungsten, gold, silver or their alloys. However, by far the most important catalyst in metallic silver or silver oxide on a support. Various oxidation promotors have been used e.V g. barium oxide or hydroxide. In addition inhibitors for carbon dioxide formation for example volatile organic halogen compounds such as ethylene dichloride can be employed in conjunction with the silver., as is well known in the art, but their effect is small and their use not necessary.

In the practice of this invention, therefore, a mixture of ethylene and air preheated to 200 C. to 250 C. of

such proportions as to be just below the lower explosive f limits is pumped into a reactor for example, reactor 1 in Figure l, passing through porous ceramic tubes either impregnated or lled with catalytic metallic silver. The thickness of the tubes, their porosity and the flow rate is adjusted so as to make the contact time 11/2 to 4 seconds. The tubes are immersed in a vessel 2 or 2a through which dilute sulfuric acid, usually about a 0.5 per cent or a l per cent solution, is flowing and the reaction mixture diffuses through the tubes into the acid. The ethylene is oxidized to ethylene oxide which is immediately hydrolyzed to ethylene glycol. The flow rate of the acid is adjusted to maintain the reaction temperature at an optimum, usually in the range from 200 C. to 300 C. The acid is cooled and recirculated. Means are, of course, provided for drawing off unreacted gaseous products. A side stream of the dilute glycol solution is continuously removed, neutralized and concentrated. Makeup dilute acide is added to replace that taken as a sidestream. The ethylene glycol so formed can be recovered by well known means.

It is understood that the cooling chamber and reactors can be of any desired shape. These can bel cylindrical, or have square or rectangular sides. The reactor size will depend upon a number of variables, one of which is the size of the cooling chamber.

Considering the variables involved it is impossible to make general statements regarding the reaction equipment. However, one skilled in the art, by simple experiment can determine the optimum reaction conditions such as air to ethylene ratio, space velocity and temperature of reaction. At such conditions the heat transfer coefficient can be measured and the optimum economical reaction chamber or tube size and the optimum coolant temperature and rate can be calculated as will be well understood by those skilled in the art. Such calculations do not constitute a part of this invention which, in one aspect, is concerned with using dilute sulfuric acid as (l) a heat transfer medium for removing the heat of reaction in the preparation of ethylene oxide, as well as (2) a hydrolyzing agent for the ethylene oxide formed in the reactor. Since the determination of the coolant temperature and reaction tube size to be used is well within the skill of the art the instant invention should not be limited thereby.

In another embodiment of the invention the cooling chamber can contain water used as both coolant and absorbent, and the ethylene glycol can be subsequently prepared by hydrolysis. Before hydrolysis, if desired, part of the ethylene oxide may be removed from solution by evaporation and recovered as a product of the process. Still other modifications and variations will occur to those skilled in the art and are deemed to be within the spirit and scope of this invention.

I claim:

l. The process of preparing ethylene glycol, which comprises the steps of partial oxidation of ethylene in a first zone in a mixture of a minor portion of ethylene gas and a major portion of air in the gaseous phase over a partial oxidation catalyst to form a gaseous effluent comprising ethylene oxide, passing said effluent directly into a second zone into an aqueous liquid absorbent and coolant containing a minor portion of a hydration catalyst with said second zone disposed in direct heat exchange relation to and having a common boundary with the major portion of said first Zone, hydrating said ethylene oxide to ethylene glycol in said liquid absorbent, supplying sutiicient liquid absorbent to said hydration step in said second zone to remove the heat generated by said partial oxidation in said` rst zone and thereby heat said hydration step in said second zone, removing a similar amount of liquid eiuent from said hydration step in said second zone to a third zone, and recovering etheylene glycol therefrom.

2. The process of preparing ethylene glycol, which comprises the steps of partial oxidation of ethylene in a first zone in a mixture of a minor portion of ethylene gas and a major portion of air in the gaseous phase over a partial oxidation catalyst at a temperature of from to 400 C. to form a gaseous eliuent comprising ethylene oxide, passing said efliuent directly into a second zone into an aqueous liquid absorbent `and coolant containing a minor portion of a hydration catalyst with said second zone disposed in direct heat exchange relation to and having a common boundary with the major portion of said rst zone, hydrating said ethylene oxide to ethylene glycol in said liquid absorbent, supplying sufficient liquid absorbent to said hydration step in said second zone to remove the heat generated by said partial oxidation in said first zone and thereby heat said hydration step in said second zone, removing a similar amount of liquid effluent from said hydration step in said second zone to a third zone, and recovering ethylene glycol therefrom.

3. The process of preparing ethylene glycol, which comprises the steps of partial oxidation of ethylene in a first zone in a mixture of a minor portion of ethylene gas and a major portion of air in the gaseous phase below the lower explosive limit of 3.4 volume percent ethylene over a partial oxidation catalyst to form a gaseous eluent comprising ethylene oxide, passing said efuent directly into a second zone into an aqueous liquid absorbent and coolant containing a minor portion of a hydration catalyst with said second zone surrounding and disposed in direct heat exchange relation to and having a common boundary with the major portion of said first zone, hydrating said ethylene oxide to ethylene glycol in said liquid absorbent, supplying suicient liquid absorbent to said hydration step in said second zone to remove the heat generated by said partial oxidation in said first zone and thereby heat said hydration step in said second zone, removing a similar amount of liquid eiuent from said hydration step in said second zone to a third zone, and recovering ethylene glycol therefrom.

4. The process of preparing ethylene glycol, which comprises the steps of partial oxidation of ethylene in a first zone in a mixture of a minor portion of ethylene gas and a major portion of air in the gaseous phase below the lower explosive limit of 3.4 volume per cent ethylene over a partial oxidation catalyst at a temperature of from 100 to 400 C. to form a gaseous effluent comprising ethylene oxide, passing said eiuent directly into a second zone into an aqueous liquid absorbent and coolant containing a minor portion of a hydration catalyst with said second zone surrounding and disposed in direct heat exchange relation to and having a common boundary with the major portion of said first zone, hydrating said ethylene oxide to ethylene glycol in said liquid absorbent, supplying suicient liquid absorbent to said hydration step in said second zone to remove the heat generated by said partial oxidation in said first zone and thereby heat said hydration step in said second zone, removing a similar amount of liquid effluent from said hydration step in said second zone to a third zone, and recovering ethylene glycol therefrom.

References Cited in the le of this patent UNITED STATES PATENTS 6 Cohen et al. Sept. 9, 1941 Gardner Jan. 9, 1945 Goldsby et a1. ---2 Nov. 30, 1948 Sullivan Feb. 17, 1953 FOREIGN PATENTS Great Britain MayV 4, 1923 

1. THE PROCESS OF PREPARING ETHYLENE GLYCOL, WHICH COMPRISES THE STEPS OF PARTIAL OXIDATION OF ETHYLENE IN A FIRST ZONE IN A MIXTURE OF A MINOR PORTION OF ETHYLENE GAS AND A MAKOR PORTION OF AIR IN THE GASEOUS PHASE OVER A PARTIAL OXIDATION CATALYST TO FORM A GASEOUS EFFLUENT COMPRISING ETHYLENE OXIDE, PASSING SAID EFFLUENT DIRECTLY INTO A SECOND ZONE INTO AN AQUEOUS LIQUID ABSORBENT AND COOLANT CONTAINING A MINOR PORTION OF A HYDRATION CATALYST WITH SAID SECOND ZONE DISPOSED IN DIRECT HEAT EXCHANGE RELATION TO AND HAVING A COMMON BOUNDARY WITH THE MAJOR PORTION OF SAID FIRST ZONE, HYDRATING SAID ETHYLENE OXIDE TO ETHYLENE GLYCOL IN SAID LIQUID ABSORBENT, SUPPLYING SUFFICIENT LIQUID ABSORBENT TO SAID HYDRATION STEP IN SAID SECOND ZONE TO REMOVE THE HEAT GENERATED BY SAID PARTIAL OXIDATION IN SAID FIRST ZONE AND THEREBY HEAT SAID HYDRATION STEP IN SAID SECOND ZONE, REMOVING A SIMILAR AMOUNT OF LIQUID EFFLUENT FROM SAID HYDRATION STEP IN SAID SECOND ZONE TO A THIRD ZONE, AND RECOVERING ETHYLENE GLYCOL THEREFROM. 